Electromagnetic fields from a high-field nuclear magnetic resonance (NMR) imaging instrument (Static: 2.3T; RF: 100 MHz; Gradient Field: 1.0 T/s at 1 mT; 60 min exposure at 37 degree C) are shown to enhance calcium transport in vitro in rat thymocytes and in human peripheral blood lymphocytes. Additional studies indicate that thymocytes from mature compared to juvenile rats respond more vigorously. Spectral analysis of the nuclear magnetic resonance (NMR) gradient field indicates that extremely low frequency (ELF) components at 20, 40 and 60 Hz are prominent in the NMR imaging exposure. Independently, the applicants have shown that a 60 Hz sinusoidal magnetic field can stimulate calcium transport in the rat thymocyte. These findings demonstrate for the first time that (1) high-field NMR signals can stimulate net calcium transport in the lymphocyte, particularly in the mature lymphocyte, and (2) that nonthermal ELF components in the NMR gradient field may play a role in this response. The applicants propose studies using rodent and human lymphocytes that will: (1) determine whether the static, gradient, and/or RF field(s) contribute to this calcium response, and then establish a threshold value; (2) characterize the age-dependence for rodent and human lymphocyte responses; and (3) since calcium is an important second messenger, characterize the alteration of the following membrane signal transduction events: [Ca2+]i, inositol 1,4,5-triphosphate turnover, protein kinase C activation and, importantly, whether subsequent DNA and protein synthesis is altered. This research will carefully define lymphocyte responses to electromagnetic fields associated with high-field NMR. It should assist future design efforts for emerging high-field NMR systems.